Malian soldiers patrol in a street of Diabaly (400km north of the capital Bamako). Photo: AFP

French-led troops recaptured the Islamist stronghold of Gao on Saturday, in a major boost to their 16-day offensive against al-Qaeda-linked rebels holding Mali’s vast desert north.

France’s Prime Minister Jean-Marc Ayrault said the nation’s troops were also advancing on Timbuktu, another key northern town held by the insurgents.

The seizure of Gao, the most populated town in Mali’s northern region, which is roughly the size of Texas, was announced by the French defence ministry and confirmed by Malian security sources.

France said troops from Niger and Chad “will pick up the baton” and that the mayor of Gao, Sadou Diallo, was due to return from the capital Bamako, 1,200 kilometres to the southwest.

“A first contingent of Malian, Chadian and Niger troops are presently in Gao to help secure it,” a Malian security source told news agency AFP by telephone from the town. They had been flown in from Niamey, capital of neighbouring Niger.

“The French and African forces are in 100 per cent control of the town of Gao,” another Malian security source said. “There is popular rejoicing and everyone is very happy.”

Other soldiers from Chad and Niger meanwhile were moving toward the Malian border from the Niger town of Ouallam, which lies about 100km southeast of Gao.

French-led forces had seized overnight Gao’s airport and a key bridge on the southern entrance of the town, held by the al-Qaeda-linked Movement for Oneness and Jihad in West Africa (MUJAO).

There had not been substantive fighting around Gao, said a spokesman for the French military command, but there was sporadic gunfire from “terrorist elements.”

Defence ministry sources in Paris described as “plausible” a report in Le Monde newspaper, citing military sources, that hundreds of Islamists had died since the French military intervention in Mali.

In April last year after a coup in Bamako, an alliance of Tuareg rebels who wanted to declare an independent homeland in the north and several hardline Islamist groups seized Gao, Timbuktu and Kidal.

Extremist militants quickly sidelined the Tuaregs and imposed their harsh interpretation of Islamic sharia law. Transgressors were flogged, stoned and executed, they banned music and television and forced women to wear veils.

Groups involved include al-Qaeda in the Islamic Maghreb; the MUJAO, which is an offshoot of AQIM and the homegrown group Ansar Dine.

French Prime Minister Jean-Marc Ayrault said the troops were currently “around Gao and [will be] soon near Timbuktu,” further west. A fabled caravan town on the edge of the Sahara desert, Timbuktu served as a centre of Islamic learning for centuries.

“The objective is that the African multinational force being put together be able to take over, and that Mali be able to begin a process of political stabilisation,” Ayrault said.

West African defence chiefs meanwhile reviewed the slow deployment of regional forces to bolster the French-led offensive at an emergency meeting in Ivory Coast boosting their troop pledges to 5,700 from the previous 4,500.

Chad, which neighbours Mali but is not a member of the Economic Community of West African States raising that force, has separately promised 2,000 soldiers.

A fraction of the African forces has arrived in Bamako, the Malian capital in the south of the country, and is slowly deploying elsewhere. So far, however, French and Malian forces have done all the fighting.

France has already deployed 2,500 troops to Mali and its defence ministry says 1,900 African soldiers are on the ground there and in Niger.

US Defense Secretary Leon Panetta told his French counterpart, Jean-Yves Le Drian, in a phone conversation Saturday the Pentagon was ready to offer its vast fleet of aerial refueling tankers to back up French forces in Mali, spokesman George Little said in a statement.

Panetta and Le Drian discussed US military support "to deny terrorists a safe haven in Mali", he said.

"Secretary Panetta informed Minister Le Drian that US Africa Command will support the French military by conducting aerial refueling missions as operations in Mali continue," Little said.

They also discussed plans for the Americans to transport troops from African nations, including Chad and Togo, to support the international effort in Mali, he added.

President Barack Obama has expressed clear support for the French operation.

Aid agencies have shown concern about the growing food crisis for civilians in the vast semi-arid north of Mali and the drought-stricken Sahel as a whole.